JPH0551467A - Polypropylene biaxially orientated film having excellent high-temperature electric characteristic - Google Patents

Abstract

PURPOSE:To obtain a biaxially orientated film of polypropylene having high dielectric breakdown strength and slight reduction in dielectric breakdown strength even at high temperature. CONSTITUTION:100 pts.wt. polypropylene resin is blended with 0.1-10 pts.wt. silane compound shown by the general formula YRSiX3 (Y is methacryloxy group; R is bifunctional alkyl group bonded to 1-4 methylene groups; X3 are mutually same as or different from each other and hydrolyzable monofunctional organic groups) to give a biaxially orientated film of polypropylene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polypropylene biaxially stretched film having excellent high temperature electrical properties, and more particularly to a polypropylene biaxially stretched film having a high dielectric breakdown voltage and a small decrease in the dielectric breakdown voltage at high temperatures.

[0002]

BACKGROUND OF THE INVENTION Polypropylene is widely used as an electrically insulating material such as a capacitor because of its excellent electrical, mechanical and chemical properties. One of the important electrical properties in this field is the breakdown voltage. The dielectric breakdown voltage is a voltage per unit thickness of a film, which is a voltage at which a relatively large current flows when an insulator is broken and the insulation resistance is reduced. In order to increase the dielectric breakdown voltage, a polypropylene resin having specific physical properties, such as a polypropylene resin having a constant relationship between the molecular weight and the intrinsic viscosity (Japanese Patent Laid-Open No. 59-63611), and the molecular weight and the molecular weight distribution are limited. It has been proposed to use a polypropylene resin (JP-A-59-63608) or a polypropylene resin having a limited crystallization temperature and a crystallization rate (JP-A-58-181616) as a biaxially stretched film.

[0003]

[Problems to be Solved by the Invention] However, when the above-mentioned polypropylene resin is used, the dielectric breakdown voltage of the biaxially stretched film near room temperature (for example, 23 ° C) is high, but at high temperature (for example, around 80 ° C). The breakdown voltage at () significantly decreases.

The condenser generates a little heat due to repeated storage and discharge, and in actual use, the temperature becomes considerably higher than room temperature. Therefore, when a polypropylene biaxially stretched film is used as a capacitor, the dielectric breakdown voltage decreases due to the temperature rise, which causes problems such as adversely affecting the performance of the capacitor. A film having a high dielectric breakdown voltage at a high temperature, which is improved from these, has been desired.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above-mentioned problems, the present inventors have found that the addition of a specific silane compound to a polypropylene resin can solve such problems. The invention has been completed.

That is, according to the present invention, the breakdown voltage under DC voltage at 23 ° C. is 500 V / μm or more, and the breakdown voltage under DC voltage at 80 ° C. with respect to the breakdown voltage under DC voltage at 23 ° C. It is a polypropylene biaxially stretched film having a voltage ratio of 0.8 or more and excellent in high temperature electrical characteristics.

The present invention will be described below by detailing its manufacturing method.

The present invention relates to 100 parts by weight of a polypropylene resin represented by the following general formula (2): wherein Y is a methacryloxy group, R is a divalent alkyl group having 1 to 4 methylene groups bonded, and X is mutually A monovalent organic group which is the same or different and is hydrolyzable is shown.)

[0009]

## STR2 ## A polypropylene biaxially stretched film comprising 0.1 to 10 parts by weight of a silane compound represented by YRSiX ₃ .

The polypropylene resin in the present invention means
Propylene homopolymer or propylene and ethylene, α
-Copolymers with olefins are also included, and among them, propylene homopolymers and propylene / ethylene copolymers are preferably used, and propylene homopolymers are particularly preferable.

The term α-olefin as used herein means butene-
1, pentene-1, hexene-1, heptene-1, octene-1, 3-methylbutene-1, 4-methylpentene-1, vinylcyclohexane, styrene and the like.

As a method for producing these polypropylene resins, for example, a solvent polymerization method using an inert medium, a bulk polymerization method in which an inert medium is substantially absent, or a gas phase polymerization method can be used. Treating a catalyst system of titanium trichloride obtained by reducing titanium tetrachloride with metallic aluminum and an organoaluminum compound, or a titanium trichloride composition obtained by reducing titanium tetrachloride with an organoaluminum compound with a specific ether compound After that, a catalyst system comprising a titanium trichloride composition further treated with titanium tetrachloride and an organoaluminum compound, or a catalyst obtained by supporting a titanium halide on a magnesium halide carrier, and a catalyst comprising an organoaluminum compound A system etc. are mentioned. The polymer slurry obtained in such a polymerization system is decomposed with a solvent such as alcohol to remove the catalyst residue and washed with water, and then the slurry is removed by a centrifuge method or the like to remove the atactic polymer content, or propylene. In the bulk polymerization method using itself as the liquid medium, there is a method of removing the catalyst residue and atactic polymer content by washing and replacing the obtained polymer slurry with propylene.

In addition to the method in which the bulk polymerization is carried out alone, or in combination with the gas phase polymerization or after carrying out the gas phase polymerization alone, it is reslurried in an inert medium such as hexane or heptane, and the catalyst residue is removed with alcohol or the like. There is also a method of decomposing and washing and removing.

When the polypropylene resin thus obtained is used as an electrical insulating material, it is polymerized using the above-mentioned catalyst which gives highly stereoregular polypropylene, and the catalyst residue and atactic polymer content are obtained from the obtained polymer. Strictly removed isotactic index of polymer (boiling of polymer measured by Soxhlet extractor n-
Heptane extraction residue rate: weight of unextracted polymer / weight of unextracted polymer expressed as a percentage, hereinafter abbreviated as II) is 94%
Or more, preferably 96% or more, the melt index of pellets at 230 ° C (based on ASTM D-1238, hereinafter abbreviated as MI) is 0.3 to 30 g / 10 min, and total ash content (constant in the magnetic crucible) A polypropylene resin having a content of 50 ppm or less, preferably 30 ppm or less, which is obtained by melting and vaporizing the polymer so that the polymer does not ignite, and then showing the residue when completely ashed in an electric furnace is expressed as a ratio to the charged polymer) is preferably used.

The silane compound used in the present invention is represented by the following general formula:

[0016]

Embedded image represented by YRSiX _3, in the formula, Y is methacryloxy group having carbon-carbon double bond capable of reacting with polypropylene, R represents a methylene group linking the methacryloxy group and a silicon atom 1-4
Individual linearly bonded divalent alkyl groups, X is a hydrolyzable monovalent organic group, and three X groups may be the same or different from each other.

Examples of these silane compounds include γ
-Methacryloxypropyltris (trimethylsiloxy) silane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and the like, among which γ-methacryloxypropyltrimethoxysilane is preferably used.

The content of these silane compounds is 0.1 to 10 parts by weight with respect to 100 parts by weight of polypropylene resin,
It is preferably 0.5 to 3 parts by weight. When the content of the silane compound is less than 0.1 part by weight, the effect of the invention is small, and 10
Even if it is contained in excess of parts by weight, further increase in the dielectric breakdown voltage can hardly be expected, which causes processing problems, increases in cost, and is uneconomical.

In addition to the above-mentioned components, antioxidants, neutralizing agents, heat stabilizers, organic peroxides, etc. may be added according to the application, to the extent that the effects of the present invention are not significantly impaired. Among these, by adding an organic peroxide, it is possible to improve the MI of the resin composition while improving the moldability while maintaining the effects of the invention.

Examples of organic peroxides are t-butylperoxyisopropyl carbonate, 2,2-di- (t-butylperoxy) -butane, 2,5-dimethyl-2,5-di- (t -Butylperoxy) -hexane and the like, among them 2,5-dimethyl
-2,5-di- (t-butylperoxy) -hexane is preferred.

In this way, according to the present invention, the polypropylene resin, the silane compound, and various additives as necessary are added and blended using a known mixer such as a Henschel mixer, and then pelletized using an extruder. The composition is obtained as a polypropylene biaxially stretched film composition, but the above additives are not all compounded with a Henschel mixer or the like, for example, a liquid substance or the like is added from a hopper port or a vent port of an extruder. Does not prevent the achievement of the present invention. Further, a method in which pellets containing a high concentration of a silane compound are prepared in advance, polypropylene resin pellets containing no silane compound are mixed and diluted, and pelletized again by an extruder can also be applied.

As a method for obtaining a biaxially stretched film from the above-mentioned composition, a pellet is formed into a sheet having an appropriate thickness, and then a polypropylene resin which is generally used such as a tenter method or a tubular method is used. Axial stretching method can be applied,
There is no particular limitation. For example, either a sequential biaxial stretching method in which one direction is stretched and then the other direction is stretched, or a simultaneous biaxial stretching method in which two directions are simultaneously stretched can be applied.

[0023]

The present invention will be described in detail below with reference to examples. In the following description: II:% (boiling n- measured by Soxhlet extractor
Heptane extraction residual rate. ) ・ MI: g / 10min (conforms to ASTM D-1238.) ・ Total ash content: ppm (residual ash content obtained by melting and vaporizing polymer) ・ Dielectric breakdown voltage: V / μm (conforms to JIS-2330).

Example 1 Obtained by polymerizing propylene using a catalyst system of titanium trichloride obtained by reducing titanium tetrachloride with metallic aluminum in a solvent polymerization method using heptane and an organoaluminum compound. Propylene homopolymer A produced by a method in which the catalyst heptane slurry of the obtained polymer was decomposed with methanol to remove the catalyst residue, washed with water, and then the heptane slurry of the polymer was centrifuged to remove the atactic polymer component. MI 1.4g / min, II 97.5%, total ash 20ppm) 1
0.40 parts by weight of a phenolic antioxidant with respect to 00 parts by weight,
0.005 parts by weight of a stearic acid metal salt neutralizing agent and 3 parts by weight of γ-methacryloxypropyltrimethoxysilane (manufactured by Nippon Unica Co., Ltd.) as a silane compound were added and mixed with a Henschel mixer, and then 250 using an extruder. Pelletized at ° C. The pellets were then extruded at 250 ° C and
A sheet of 550 μm was obtained. Using a TM long biaxial stretching machine, this sheet was first subjected to 5 MD direction at 150 ° C.
Thickness and then 7 times in the TD direction
A 15 μm biaxially stretched film was obtained. The dielectric breakdown voltage (hereinafter abbreviated as BDV) of the thus obtained biaxially stretched film at 80 ° C. and 23 ° C. was measured.
526 V / μm and 573 V / μm, BDV80 ° C / BDV23
The ℃ ratio was 0.918, which was good. The results are shown in Table 1.

Example 2 As Example 1 except that 0.25 parts by weight of 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane (manufactured by Yoshitomi Pharmaceutical Co., Ltd.) was added as an organic peroxide. I went the same way. The results are shown in Table 1.

Example 3 Example 3 was repeated except that the addition amount of γ-methacryloxypropyltrimethoxysilane was changed to 0.5 part by weight.
The results are shown in Table 1.

Example 4 Example 3 was repeated except that 0.0167 part by weight of 2,5-dimethyl-2,5-di- (t-butylperoxy) -hexane was added as an organic peroxide. The results are shown in Table 1.

Comparative Example 1 The same procedure as in Example 1 was carried out except that γ-methacryloxypropyltrimethoxysilane was not added.
Since the value of 80 ℃ is low, the ratio of BDV80 ℃ / BDV23 ℃ is 0.74
It was 2. The results are shown in Table 1.

Example 5 In a solvent polymerization method using heptane, a titanium trichloride composition obtained by reducing titanium tetrachloride with an organoaluminum compound was treated with a specific ether compound and then further treated with titanium tetrachloride. Polymerizing propylene using a treated titanium trichloride composition and a catalyst system of an organoaluminum compound,
Propylene homopolymer B (MI 0.4 g / 10 min, produced by a method of decomposing a catalyst residue of the obtained slurry with methanol, washing with water and further removing the atactic polymer by centrifuging the heptane slurry. II is 99.5
%, Total ash content 10 ppm) was used instead of the propylene homopolymer A, and the same procedure as in Example 1 was carried out. The results are shown in Table 1.

Example 6 Obtained by copolymerizing propylene and ethylene in a bulk polymerization method using a catalyst system of a carrier obtained by supporting titanium tetrachloride on magnesium halide and an organoaluminum compound. The propylene / ethylene copolymer (ethylene content 0.5 wt%, MI 4.4 g / 10 min, II 97.0) produced by a method of removing the catalyst residue and atactic polymer content by propylene washing displacement of the obtained copolymer slurry.
%, The total ash content is 28 ppm) was used in the same manner as in Example 1 except that the propylene homopolymer A was used. The results are shown in Table 1.

Example 7 The procedure of Example 4 was repeated, except that the propylene homopolymer A was replaced by the propylene / ethylene copolymer obtained in Example 6. The results are shown in Table 1.

Comparative Example 2 The procedure of Example 1 was repeated except that the propylene / ethylene copolymer obtained in Example 6 was used and that γ-methacryloxypropyltrimethoxysilane was not added. The results are shown in Table 1.

[0033]

[Table 1]

[0034]

The polypropylene biaxially stretched film obtained by the present invention has a high dielectric breakdown voltage of 500 V / μm or more under a direct current voltage at a high temperature, and has excellent electric characteristics, and therefore has an excellent electrical insulating material. And is industrially superior.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical display location B29K 105: 34 B29L 7:00 4F C08L 23:10 (72) Inventor Kazuhiro Masuda Takaishi City, Osaka Prefecture 1-6 Takasago Mitsui Toatsu Kagaku Co., Ltd.

Claims (2)

[Claims] 1. The breakdown voltage under DC voltage at 23 ° C.
Polypropylene resin excellent in high-temperature electrical characteristics, which is 500 V / μm or more and has a ratio of the dielectric breakdown voltage under a DC voltage of 80 ° C. to the dielectric breakdown voltage under a DC voltage of 23 ° C. of 0.8 or more. Axial stretched film. 2. 100 parts by weight of a polypropylene resin and the following general formula 1 (wherein Y is a methacryloxy group, R is a divalent alkyl group having 1 to 4 methylene groups bonded, and X are the same or different from each other. A monovalent organic group capable of being hydrolyzed is shown below.) The biaxially oriented polypropylene film according to claim 1, which comprises 0.1 to 10 parts by weight of a silane compound represented by YRSiX ₃ .